The invention relates to a method of preparing a polyamide acid, used for processing of semiconductors, obtained from a diamine and a tetracarboxylic acid dianhydride, optionally with a diaminocarbonamide compound.
More particularly, it is to provide a polyamide acid for processing of semiconductors capable of transforming into a polyimide resin, having imide rings and/or benzoylenequinazolone rings, useful as insulating films for semiconductors such as a surface-protecting film of semiconductors or layer-insulating film of semiconductors having multi-layer construction.
Heretofore, silicon dioxide films which were formed by the chemical gas-phase growing method have mainly been employed as insulating films for semiconductors, such as surface-protecting films of semiconductors or layer-insulating films of wired conductors having multi-layer wiring construction.
However, silicon dioxide films have defects. There is a tendency to crack due to stress of films if they are thick in size or if they are used for layer-insulating films of a wired conductor having more than three layers. Snapping of wired conductors also tends to occur due to their poor step coverage.
These defects have prevented improvements in efficiency and integration of semiconductors.
In order to overcome these defects, there have been recently employed, as insulating films, organic materials, particularly polyimide group resins having imide rings and/or benzoylenequinazolone rings obtained by heating and dehydrating a polyamide acid synthesized from a diamine and a tetracarboxylic acid dianhydride optionally with a diaminocarbonamide. Such films have superior heat-resistance.
By using the materials, the defects of silicon dioxide films such as occurrence of cracks and poor step coverage have been avoided, and thus novel semiconductor apparatus have been invented as disclosed in Japanese patent publications Nos. 51-44871/1976 and 51-31185/1976 and the respective corresponding U.S. Pat. No. 3,846,166 and No. 4,017,886.
The above-mentioned insulating film of a polyimide group resin having imide rings and/or benzoylenequinazolone rings may be formed by preparing a polyamide acid from a diamine and a tetracarboxylic acid dianhydride optionally with a diaminocarbonamide, then making a solution of the thus obtained polyamide acid with an inert solvent, thereafter coating the solution on a wafer with a photoresist rotatory coating machine, and finally heating the coated wafer.
The insulating film must be formed uniformly with a thickness of below 5 .mu.M and within the range of .+-.0.2 .mu.M scattering, and without any pin holes caused by runaway (repelling) of coated film from viewpoint of the capabilities of semiconductors.
It must also have heat-resistance enough for withstanding heat-processing applied during production of semiconductors, such as wire bonding and contact alloy processing between electrodes.
However, there have taken place such problems in the course of trial manufacture of many semiconductors, in which the above-mentioned polyamide acid was used, that a uniform film with sufficient thickness could not be formed. Pin holes due to runaway of coated film developed and the desired heat-resistance could not be obtained.